Sleep apnea occurs when a person stops breathing during sleep. An apnea may be defined as the cessation or reduction of airflow for a certain period of time. Apneas may lead to decreased blood oxygenation and thus to the disruption of sleep. With some apneas, the airway is open, and the patient is merely not attempting to breathe. With other apneas, the airway is closed. The airway may also be partially obstructed (i.e., narrowed). This may also lead to decreased ventilation, decreased blood oxygenation, and/or disturbed sleep.
A common form of treatment for apneas is the administration of Continuous Positive Airway Pressure (CPAP). CPAP treatment acts as a pneumatic splint of the airway by the provision of a constant positive pressure to the patient usually in the range 3 to 20 centimeters of water (cm H2O). Another form of treatment for apneas is the administration of bi-level (or “BiPAP”) treatment. With bi-level treatment, one pressure level is provided while a patient is inhaling and a second, generally lower, pressure level is provided while the patient is exhaling. CPAP and bi-level treatments may be applied over a predetermined period of time, where the pressure applied to a patient is “ramped up” over time. For instance, a patient may begin the sleep process with a pressure being applied at one value and the pressure may be gradually raised to a second pressure over a predetermined ramp time (e.g., less than forty-five minutes). The purpose of such ramp up process is to allow the patient to fall asleep while a relatively low pressure is being applied, and raise the pressure to the treatment pressure after the patient is asleep in order to treat apnea-type events. The higher, treatment level pressure is generally not applied while the patient is awake because it may be uncomfortable for the patient and may hinder the patient's ability to fall asleep. However, the time it takes for a patient to fall asleep (referred to as “latency”) may be highly variable from night to night and/or from patient to patient. In some instances, the patient may fall asleep and experience apnea before the pressure has ramped up to the treatment pressure level, in which case the pressure may be insufficient to prevent or treat the apnea. In other instances, the patient may still be awake when the pressure has ramped up to the treatment pressure level (or other relatively high pressure), which may be uncomfortable and which may hinder the patient's ability to fall asleep, as discussed above.
With both CPAP and bi-level therapy, pressurized air is supplied to the airway of the patient by a motor driven blower (or other suitable gas delivery system) that delivers the pressurized air through a connection system (e.g., a breathing circuit or air delivery hose) to one or more breathing passages of the patient (e.g., the patient's nose and/or mouth) via a mask sealingly engaged against the patient's face. An exhaust port may be provided proximate to the mask to allow exhaled gasses to escape. The mask can take various forms, e.g., a nose, mouth, or face mask, nasal prongs, pillows or cannulae.